Ok, I have an OTTB, which as we all know are notorious for horribly thin tails. Hahaha what works for me and him (over time) is Enfusium volume shampoo/conditioner and Enfusium rejuvenation spray. Both are safe to use repeatedly and I use the rejuvenation spray every single time I brush his tail to reduce breakage. It has worked very well so far! You can buy it at any Walmart in the hair care aisle :) ENFUSIUM! It comes in a grey bottle and there are several types, choose as needed :)
Horses are angels without wings!